Calcium enriched refractory material by the addition of calcium carbonate

ABSTRACT

The composition applied to the refractory structure has a magnesia-based refractory material, calcium carbonate and a binder. After application of the refractory material to a refractory structure and upon application of heat to the applied refractory material a matrix is formed which protects against penetration of the slag into the refractory material. The resulting refractory material has improved hot strength, slag resistance and durability.

BACKGROUND OF THE INVENTION

The present invention relates to refractory material for applying to arefractory structure and a method of applying the refractory material toa refractory structure or lining. More particularly, the invention isdirected to preserving or maintaining refractory structures or liningsfrom mechanical erosion and/or attack by corrosive materials such asthose produced during manufacture of metals or metal alloys includingacid and basic slags. The refractory linings also are exposed to thermalshock which can cause premature failure of the refractory.

SUMMARY

The present invention is directed to a composition of a refractorymaterial and a method of coating a refractory structure, particularly ahot refractory structure using the refractory material. The refractorymaterial can be applied to a refractory structure such as a vessel orladle. The composition of the refractory material which applied to therefractory structure comprises from about 20 to about 95 weight percentmagnesia-based refractory material, from about 2.0 to about 10 weightpercent calcium carbonate and from about 0.1 to about 5 weight percentof a binder such as organic acid, alkali silicate or alkali phosphate.

Heat from the furnace or vessel which contacts the refractory materialon the refractory structure accelerates the hardening and curing of therefractory material of the present invention by transmission of heat tothe refractory material so as to form a high density matrix ofrefractory material. The applied refractory material passes from theplastic state to a nonplastic or substantially rigid and nonpliablestate in its final form in which the above mentioned high density matrixis present. The calcium carbonate in the refractory material is calcinedin place upon transfer of the heat from the furnace or vessel which isbeing processed in the refractory structure to which the refractorymaterial is applied. Carbon dioxide gas evolves therefore after therefractory material is no longer in the plastic state. The refractorymaterial forms a high density matrix which protects against penetrationof slag and molten metal.

In the present invention the calcium carbonate calcines in place whichleaves a very reactive source of calcia within the matrix of therefractory mass. In the present invention the coarsest calcium carbonatecan be ATF-20 which has a particle size distribution that starts below0.85 mm. The very fine calcium carbonate of the present invention can beVicron® 15-15 limestone product which has a particle size distributionthat starts below 15 microns (0.015 mm). In the present invention finecalcium carbonate is added to be reactive with the magnesia grains andany infiltrating slag, not as a coarse particle size distribution forthermal shock resistance.

In another embodiment the magnesia-based refractory material of thecomposition of the refractory material is present in an amount fromabout 20 to about 95 weight percent.

In another embodiment the magnesia-based refractory material of thecomposition of the refractory material is present in an amount fromabout 60 to about 88 weight percent.

In another embodiment the calcium carbonate of the composition of therefractory material is present in at least two different particle sizedistributions. A fine form of calcium carbonate is present in an amountof from about 3.5 to about 4.5 weight percent and a coarser form calciumcarbonate is present in an amount of from about 3.5 to about 4.5 weightpercent.

In another embodiment the calcium carbonate of the composition of therefractory material is present in at least two different particle sizedistributions. A fine form of calcium carbonate is present in an amountof from about 2.5 to about 3.5 weight percent and a coarser form ofcalcium carbonate is present in an amount of from about 2.5 to about 3.5weight percent.

In another embodiment the composition of the refractory material furthercomprises from about 0.2 to about 8 weight percent calcium hydroxide.

In another embodiment the composition of the refractory material furthercomprises from about 0.1 to about 2.0 weight percent of a plasticizersuch as bentonite.

In another embodiment the composition of the refractory material furthercomprises from about 0.1 to about 1.0 weight percent of a dispersantsuch as citric acid.

The refractory material can be applied by a gunning system.

After the high density matrix of the refractory material has beenformed, a layer of the refractory material protects the refractorystructure to which the refractory material has been applied againstattack by corrosive materials such as molten slags and molten metals,especially against attack by acid and basic slags, and steel.

In the method of the invention, application of the refractory materialcan be applied to provide a layer of refractory material of a thicknessof about 1 inch to about 12 inches both prior to exposing as well asafter exposing the lining to corrosive materials. Desirably, applicationof the refractory material is performed prior to initial exposure of therefractory lining to the corrosive materials, and can be repeated aftereach exposure of the lining to those corrosive materials. Depending onthe degree of erosion, corrosion or penetration of corrosive materialsinto the applied refractory material, the refractory material of thepresent invention need not be reapplied to the refractory material afterevery contact of corrosive materials with the refractory material.

Application of the refractory material can be performed while therefractory material is at a temperature of about 32 degrees F. to about2500 degrees F.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail by reference to thefollowing specification and non-limiting examples. Unless otherwisespecified, all percentages are by weight and all temperatures are indegrees Fahrenheit.

The composition applied to the refractory structure comprises from about20 to about 95 weight percent of a magnesia based refractory materialsuch as magnesia, from about 2.0 to about 10 weight percent calciumcarbonate, and from about 0.1 to about 5.0 weight percent of a bindersuch as organic acid, alkali silicate or alkali phosphate.

Heat from the furnace which contacts the refractory material on therefractory structure accelerates the hardening and curing of therefractory material of the present invention by transmission of heatfrom the underlying refractory structure to the refractory material soas to form a high density matrix of refractory material. The appliedrefractory material passes from the plastic state to a nonplastic orsubstantially rigid and nonpliable state in its final form in which theabove mentioned high density matrix is present. The calcium carbonate inthe refractory material is calcined in place upon transfer of the heatfrom the refractory structure itself. Carbon dioxide gas evolvestherefore not while the refractory material is in a plastic state. Therefractory material forms a high density matrix which protects againstpenetration of slag and molten metal. The calcium from the calciumcarbonate forms CaO or calcia which enriches the matrix phase of therefractory material which is where initial slag penetration would occur.

The use of calcium carbonate as a source of CaO (calcia) is desirablebecause it does not significantly react with water (hydrate ordecompose) or other refractory constituents during the mixing with wateror subsequent refractory material application. If calcium oxide were tobe used instead of the calcium carbonate, the calcium oxide wouldrapidly react with water and/or other bond components so as to disruptthe integrity of the applied mass which would result in poor durabilityof the applied refractory. The calcium carbonate in the presentinvention calcines upon exposure to heat to form reactive calcium oxide.When slag comes in contact with this calcium oxide the calcium oxidereadily reacts with the slag to produce high melting point compoundssuch as dicalcium silicate. These compounds thicken and or solidify theslag so as to prevent further penetration of the slag into the body ofthe refractory. This mechanism reduces corrosion of the refractorythereby extending the service life of the refractory.

The refractory material can be applied through any batch or continuousfeed gunning system. The refractory material has good slag and erosionresistance. The material is suitable for use for the maintenance ofelectric are furnaces, basic oxygen furnaces, and other metallurgicalvessels or ladles. The refractory material can be applied manually usinghand tools.

The wetting agent for a gunning composition of the magnesia basedrefractory material can be any suitable dispersant, superplasticizer,anionic, cationic or nonionic surfactant, the selection of which for anyparticular composition would be understood by one of ordinary skill inthe art of refractories.

Heat which is applied to the refractory composition of the presentinvention contributes to the forming of a high density matrix ofrefractory material. A magnesia based refractory composition results,having improved physical properties, at temperatures from about 230degrees F. to about 3200 degrees F. over compositions currently used forproduction or repair of refractory furnace linings.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The following embodiments are, therefore, to beconstrued as merely illustrative, and not limitative of the remainder ofthe disclosure in any way whatsoever.

Magnesia, i.e., MgO, for the refractory material of the presentinvention can be derived from sources such as natural, seawater or brinemagnesite, or mixtures thereof. The magnesia preferably is dead burnedmagnesia. By “dead burned” magnesia is meant magnesia fired to hightemperatures to produce refractory grains with reduced reactivity withwater and impart a degree of hydration resistance to the refractorygrains which are formed substantially completely of well-sintered, lowporosity crystals to distinguish them from reactive lower temperaturecalcined caustic magnesite. Such materials are commercially available inpurities of from about 60 to about 99 weight percent magnesia.

Plasticizers useful in the refractory compositions include but are notlimited to clays such as ball clay, kaolinite, or bentonite, aluminumhydroxide, and starch preferably bentonite.

High temperature binders useful in the refractory compositions includebut are not limited to alkali phosphates such as sodium phosphate,potassium phosphate, ammonium phosphate, magnesium phosphate, calciumphosphate, and alkali silicates such as sodium silicate, potassiumsilicate, magnesium silicate, calcium silicate, and sulfates such assodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate,ammonium sulfate, zirconium sulfate, aluminum sulfate and sulfamic acid.Preferred binders include sodium silicate, sodium phosphate and sulfamicacid. These plasticizers and high temperature binders are commerciallyavailable.

In the present invention the amount of calcium carbonate present can befrom about 2.0 to about 10 weight percent of the total refractory blend.Use of weight percentages of calcium carbonate of more than about 10weight percent is limited by the inability of the calcium carbonate tointegrate itself into a resultant refractory matrix which is formedafter heat is applied to the refractory blend. Use of weight percentagesof calcium carbonate of less than about 2.0 weight percent of calciumcarbonate is limited by the inability of the calcium carbonate to be apart of a high density matrix in the refractory material which inhibitspenetration of slag into the matrix.

The calcium carbonate of the present invention can be of two differentparticle size distributions such as a very fine portion and a coarserportion. A coarser portion of calcium carbonate can be a calciumcarbonate such as ATF-20 screened limestone product available fromSpecialty Minerals Inc. of Bethlehem, Pa. ATF-20 screened limestoneproduct has only a trace amount of particles larger than 20 mesh (0.85mm), about 15 weight percent larger than 40 mesh and about 75 weightpercent larger than 100 mesh and about 92 weight percent larger than 200mesh. A very fine portion of calcium carbonate can be a calciumcarbonate such as Vicron® 15-15 ground limestone product available fromSpecialty Minerals Inc. of Bethlehem, Pa. Vicron 15-15 ground limestonehas only about 0.004 weight percent of particles larger than 325 meshand an average particle size of 3.5 microns.

In another embodiment the calcium carbonate of the composition of therefractory material is present as a single particle size distribution. Avery fine form of calcium carbonate is present in the refractorymaterial in an amount of from about 2.0 to about 7.0 weight percent.

In another embodiment the calcium carbonate of the composition of therefractory material is present in at least two different particle sizedistributions. A very fine form of calcium carbonate is present in anamount of from about 3.5 to about 4.5 weight percent and a coarser formof calcium carbonate is present in an amount of from about 3.5 to about4.5 weight percent.

In another embodiment the calcium carbonate of the composition of therefractory material is present in at least two different particle sizedistributions. A very fine form of calcium carbonate is present in anamount of from about 2.5 to about 3.5 weight percent and a coarser formof calcium carbonate is present in an amount of from about 2.5 to about3.5 weight percent.

In one embodiment, the refractory material has about 3.5 to about 4.5weight percent of a very fine portion of calcium carbonate and about 3.5to about 4.5 weight percent of a coarser portion of calcium carbonate.In addition, the refractory blend can have from about 0.2 to about 5weight percent of sodium hexametaphosphate as a setting agent and hightemperature binder to provide strength and substrate adherence. Examplesof a refractory material of this embodiment is set forth in Examples 1,2 and 3.

In one embodiment, the refractory material has about 2.5 to about 3.5weight percent of a very fine portion of calcium carbonate and about 2.5to about 3.5 weight percent of a coarser portion of calcium carbonate.In addition, the refractory blend can have from about 0.2 to about 3.0weight percent of sulfamic acid as a setting agent and high temperaturebinder to provide strength and substrate adherence. An example of arefractory material of this embodiment is set forth in Example 4.

The compositions were tested in an induction furnace. The compositionsmet or exceeded the performance requirements in the areas of density,strength, drying, resistance to cracking, and durability.

Unless otherwise identified, all mesh sizes are in U.S. Mesh. As setforth below, mesh sizes are shown in a format such as 5×8 which meansparticles smaller than 5 mesh and larger than 8 mesh are present.

Example 1

Table 1 shows a refractory material for applying onto a hot or coldrefractory structure such as the slag line of a vessel or ladle. Thefollowing formulation of refractory material was dry mixed for 3 minutesafter all ingredients were in the mixer.

TABLE 1 Material Description Wt. Percent 97 grade Magnesia 5 × 8 Mesh20.00 97 grade Magnesia 8 × 18 Mesh 28.00 97 grade Magnesia −18 Mesh28.70 97 grade Magnesia Powder 12.00 Bentonite Powder 0.80 Very FineCalcium Carbonate Vicron ® 15-15 4.00 ground limestone Coarser CalciumCarbonate ATF-20 4.00 Sodium Silicate Powder 1.00 Citric Acid Powder0.50 Sodium hexametaphosphate Powder 1.00

Example 2

Table 2 shows a refractory material for applying onto a hot or coldrefractory structure such as the slag line of a vessel or ladle. Thefollowing formulation of refractory material was dry mixed for 3 minutesafter all ingredients were in the mixer.

TABLE 2 Material Description Wt. Percent 90 grade Magnesia 5 × 8 Mesh20.00 90 grade Magnesia 8 × 18 Mesh 28.00 90 grade Magnesia −18 Mesh28.70 90 grade Magnesia Powder 12.50 Bentonite Powder 0.80 Very FineCalcium Carbonate Vicron ® 15-15 4.00 ground limestone Coarser CalciumCarbonate ATF-20 limestone 4.00 Sodium Silicate Powder 1.00 Citric AcidPowder 0.50 Sodium hexametaphosphate Powder 0.50The sodium silicate of the above Example 2 is hydrated sodium silicatePyramid P60 having a SiO₂ to Na₂O ratio of 3.3.

Example 3

Table 3 shows a refractory material for applying onto a hot or coldrefractory structure such as the slag line of a vessel or ladle. Thefollowing formulation of refractory material was dry mixed for 3 minutesafter all ingredients were in the mixer.

TABLE 3 Material Description Wt. Percent 90 grade Magnesia 5 × 8 Mesh20.00 90 grade Magnesia 8 × 18 Mesh 28.00 90 grade Magnesia −18 Mesh28.70 97 grade Magnesia Powder 12.00 Bentonite Powder 0.80 Very FineCalcium Carbonate Vicron ® 15-15 4.00 ground limestone Coarser CalciumCarbonate ATF-20 limestone 4.00 Sodium Silicate Powder 1.00 Citric AcidPowder 0.50 Sodium hexametaphosphate Powder 1.00

Example 4

Table 4 shows a refractory material for applying onto a hot or coldrefractory structure such as the slag line of a vessel or ladle. Thefollowing formulation of refractory material was dry mixed for 3 minutesafter all ingredients were in the mixer.

TABLE 4 Material Description Wt. Percent 97 grade Magnesia 5 × 8 Mesh23.80 97 grade Magnesia 8 × 18 Mesh 35.60 97 grade Magnesia −18 Mesh12.50 97 grade Magnesia Powder 16.30 Bentonite Powder 0.80 Very FineCalcium Carbonate Vicron ® 15-15 3.00 ground limestone Coarser CalciumCarbonate ATF-20 3.00 Calcium Hydroxide Powder 2.50 Citric Acid Powder0.50 Sulfamic acid Powder 2.00

Accordingly, it is understood that the above description of the presentinvention is susceptible to considerable modifications, changes andadaptations by those skilled in the art, and that such modifications,changes and adaptations are intended to be considered within the scopeof the present invention.

1. A composition suitable for providing a refractory materialcomprising: 20 to 95 weight percent magnesia containing refractorymaterial; 0.1 to 5.0 weight percent of a binder; and 2.0 to 10 weightpercent of calcium carbonate for reacting upon exposure to heat toprovide the refractory material as a source of calcium oxide forincreasing corrosion resistance.
 2. The composition according to claim 1wherein the binder is an organic acid.
 3. The composition according toclaim 1 wherein the magnesia containing refractory material is presentin an amount of 60 to 88 weight percent.
 4. The composition according toclaim 1 further comprising calcium hydroxide in amount of 0.2 to 8.0weight percent.
 5. The composition according to claim 1 furthercomprising a plasticizer in an amount of 0.1 to 2.0 weight percent. 6.The composition according to claim 5 wherein the plasticizer isbentonite.
 7. The composition according to claim 1 further comprising adispersant in an amount of from 0.1 to 1.0 weight percent.
 8. Thecomposition according to claim 7 wherein the dispersant is citric acid.9. The composition according to claim 1 wherein the binder is sulfamicacid wherein the sulfamic acid is present in an amount of 0.2 to 3.0weight percent.
 10. The composition according to claim 1 wherein thecalcium carbonate is present in an amount of 2.0 to 7.0 weight percentwherein the calcium carbonate has a particle size of less than 325 mesh.11. The composition according to claim 1 wherein the calcium carbonateis present in a very fine portion having a particle size of less than325 mesh and a coarser portion wherein the coarser portion has aparticle size less than 20 mesh, 15 weight percent larger than 40 mesh,75 weight percent larger than 100 mesh and 92 weight percent larger than200 mesh.
 12. The composition according to claim 11 wherein the veryfine portion is present in an amount of 2.5 to 3.5 weight percent andthe coarser portion is present in an amount of 2.5 to 3.5 weightpercent.
 13. The composition according to claim 11 wherein the very fineportion is present in an amount of 3.5 to 4.5 weight percent and thecoarser portion is present in an amount of 3.5 to 4.5 weight percent.14. The composition according to claim 12 further comprising 0.2 to 3.0weight percent sulfamic acid.